Studies will continue to be concentrated on genetic regulatory mechanisms operating at the molecular level in the qa gene cluster. In recent experiments, hybrid E. coli plasmids have been constructed in which the qa-2 ion gene product, catabolic dehydroquinase, is expressed. Expression of the enzymes encoded in the other two qa structural genes has not yet been detected but additional experiments are continuing. Experiments are also underway to determine whether the product of the qa-1 ion regulatory gene (an activator protein) is required for expression of the qa-2 ion gene in E. coli. Additional evidence will be sought to support the preliminary conclusion that regulation is at the level of transcription. The ultimate aim of these studies is to determine the nucleotide sequence of Neurospora qa DNA inserted into E. coli plasmids. The sequence data combined with available amino-terminal amino acid sequence data for such of the three qa enzymes should make it possible to determine the limits of the structural genes and to identify the presence and organization of controlling regions in this eucaryotic gene cluster.